v3.10.0.1
Document and Entity Information - shares
9 Months Ended
Sep. 30, 2018
Oct. 31, 2018
Document Information [Line Items]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Sep. 30, 2018  
Document Fiscal Year Focus 2018  
Document Fiscal Period Focus Q3  
Trading Symbol DGICA  
Entity Registrant Name DONEGAL GROUP INC  
Entity Central Index Key 0000800457  
Current Fiscal Year End Date --12-31  
Entity Filer Category Accelerated Filer  
Entity Emerging Growth Company false  
Entity Small Business false  
Class A Common Stock [Member]    
Document Information [Line Items]    
Entity Common Stock, Shares Outstanding   22,788,003
Class B Common Stock [Member]    
Document Information [Line Items]    
Entity Common Stock, Shares Outstanding   5,576,775